Missile guidance systems that use laser energy for directing a missile toward a target are subject to countermeasure from the target. Typical of these systems are those employing semi-active seekers, command to line-of-sight (CLOS), and beamrider.
FIG. 1 shows a typical engagement scenario for a missile 10 which utilizes a laser semi-active seeker 12 for guidance to a target 14. A mobile vehicle 16 such as a helicoptor launches the missile toward the target. Laser energy directed from a laser designator 18 is directed to the target and reflected to the seeker 12. Aside from such commonly accepted concerns such as seeker costs, and specific laser generated target signature requirements, this guidance method suffers from susceptability to countermeasures in the form of deception signals radiated by the target. Passive seekers, not shown, are not as responsive to a laser generated signature, but are more susceptible to target signature modification such as suppression or false target generation.
FIG. 2 shows a typical engagement scenario for a CLOS missile 10A. This missile guidance method is independent of the target 14A signature, since the missile flies a straight line until impact with whatever a gunner 20 is sighting the target tracker 22 at--operation being much like a perfect rifle without ballistic drop. While it does not require a target signature (other than initial selection by a human gunner), the system still suffers a countermeasure deficiency--missile 10A must be tracked via a beacon 23 by an automatic tracker 24 which measures the angular error of the missile signature from the aiming axis. Missile tracker 24 also has the target in its field of view, allowing a smart target to provide a stronger (but false) "missile" signature and thus fool the tracker fire control into providing erroneous commands to the missile.
FIGS. 3 and 4 show a typical laser beamrider missile guidance system. This system has no seeker or missile tracker to be spoofed. At the launch site the operator 20A aims at any object or point in space desired, and a colinear laser beam, spatially encoded over its cross section, is similarly aimed from beam projector 30 by virtue of the co-linear relationship. The receiver 31 on missile 10B decodes the received signals, which are indicative of position within the beam cross section, and initiates guidance changes to correct flight to the beam center. The missile receiver, rearward looking only, is oblivious to any energy transmitted by target 14B and thus is extremely countermeasures resistant. The gunner 20A however, is still looking at the target through a type of visual optics 32, such as a television or thermal imager. If his concentration or aiming ability can be impaired the system can still be countermeasured. Two countermeasure possibilities, for example, are rapid counterfire (which may not seriously endanger the operator, but can cause sufficient apprehension to degrade aiming stability); and rapid smoke dispersal (which can cause loss of imagery to the operator or even obscure the laser communication link). By definition these countermeasure actions are rapid, initiated after launch of a missile, and therefore impractical without some means of quickly determining that a missile launch has indeed taken place. Thus, the small chance of intercepting the beamrider signal, which surrounds and bypasses the missile and impinges on the target, assumes greater significance.